<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    body>div{
      width: 200px;border: 1px solid red;
      overflow: hidden;/*解决自动高度识别为0的问题*/
    }
    div>div{width: 50px;height: 50px;}
    #d1{background-color: red;float: left}
    #d2{background-color: green;float: left;}
    #d3{background-color: blue;float: left}

    ul{
      list-style-type: none;/*去掉图标*/
      margin: 0;
      padding:0;
    }
    li{
      float: left;
      margin-right: 10px;
    }
  </style>
</head>
<body>
<div>
  <div id="d1"></div>
  <div id="d2"></div>
  <div id="d3"></div>
</div>
<p>这是个p标签</p>

<ul>
  <li><a href="">首页</a></li>
  <li><a href="">免费课</a></li>
  <li><a href="">直播课</a></li>
  <li><a href="">精品课</a></li>
  <li><a href="">线上班</a></li>
</ul>
</body>
</html>